Search results for "conduct"

Vibrational spectroscopy in soil and sediment analysis

2014

The literature concerning the use of vibrational spectroscopy for soil and sediment analysis, published in the last years, has been revised in order to provide a picture of the strengths and weaknesses of these direct techniques to characterize soil composition and properties. Many soil components as water, organic matter, like humic substances, and minerals, can be determined together with physicochemical parameters as pH, conductivity or redox potential. The main strategies to obtain sample spectra and to extract, as many as possible, useful information were evaluated, taking into account the progress on chemometrics and discussing the whole analytical process, from sampling to sample pre…

Liquid-crystalline ordering as a concept in materials science: from semiconductors to stimuli-responsive devices.

2013

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat-panel displays, their intrinsic ability to self-organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid-crystalline materials as organic semiconductors, which are solvent-processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli-responsive macroscopic shape change of cross-linked polymer networks, w…

A new improved synthesis of the 110 K bismuth superconducting phase: freeze-drying of acetic solutions

1992

Abstract Metastability has greatly hindered the separated synthesis of the high-temperature superconducting phases represented as (Bi1−x, Pbx)2Sr2Can−1CunO4 + 2n (n = 2, 2-2-1-2, Tc≈80 K, and n = 3, 2-2-2-3, Tc≈110 K). By careful control of the synthetic variables, it becomes possible to obtain the 110 K phase as the only superconducting one through processing of freeze-dried acetic solutions. This technique leads to homogeneously sized (5–10 μm) micaceous platelets of the superconducting material.

Anomalous intensity of the 335 cm−1 phonon in YBa2Cu3O7−δ

1991

Abstract We report results on Raman scattering for the intensity of the 335 cm −1 phonon of A g (pseudo B 1g ) symmetry in thin YBa 2 Cu 3 O 7−δ films on MgO and LaAlO 3 substrates. The intensity of this phonon shows a pronounced increase below 100 K and saturates at low temperatures. We also observe an additional intensity peaking at temperatures close to the superconducting transition T C . This may indicate a structural phase transition in the vicinity of T C .

Ion transport through membranes: A computer experiment

1983

Abstract Gramicidin-A is a linear pentadecapeptide antibiotic, which forms transmembrane channels; these have a number of interesting conductance characteristics [1, 2 and Refs. therein], as for example high specific ion fluxes (a single channel carries about 10 7 sodium ions/sec at 25 °C, 1 M NaCl and 100 mV transmembrane d.d.p.) have a remarkable ion selectivity among the monovalent cations. The permeability ratios with respect to sodium were found to be in following order H + (150) > NH 4 + (8.9) > Cs + (5.8) > Rb + (5.5) > K + (3.9) > Na + (1.0) > Li + (0.33). The channel is impermeable to anions and to divalent cations and it exhibits saturation and maxima in conductance as a function …

Hybrid Molecular Materials Based upon the Photochromic Nitroprusside Complex, [Fe(CN)5NO]2-, and Organic π-Electron Donors. Synthesis, Structure, and…

2000

An organic/inorganic hybrid salt is obtained by combination of the photochromic nitroprusside complex with the organic donor TTF. The organic part shows an unprecedented 2D organization formed by an orthogonal arrangement of TTF hexamers and monomers. However, the donor layers are formed by pairs of moderately interacting dimeric (TTF)22+ units surrounded by neutral TTF molecules in such a way that the charge is localized and the compound is a semiconductor. Short contacts between the organic layers and the nitroprusside anions are present that may affect the photophysical properties of the nitroprusside.

Metallic Conductivity in a Polyoxovanadate Radical Salt of Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF): Synthesis, Structure, and Physical Chara…

2004

Electrical Behaviour of Heterobimetallic [MM′(EtCS2)4] (MM′=NiPd, NiPt, PdPt) and MM′X-Chain Polymers [PtM(EtCS2)4I] (M=Ni, Pd)

2012

Herein, we report the isolation of new heterobimetallic complexes [Ni0.6Pd1.4ACHTUNGTRENUNG(EtCS2)4] (1), [NiPtACHTUNGTRENUNG(EtCS2)4] (2) and [Pd0.4Pt1.6ACHTUNGTRENUNG(EtCS2)4] (3), which were constructed by using transmetallation procedures. Subsequent oxidation with iodine furnished the MM'X monodimensional chains [Ni0.6Pt1.4ACHTUNGTRENUNG(EtCS2)4I] (4) and [Ni0.1Pd0.3Pt1.6ACHTUNGTRENUNG(EtCS2)4I] (5). The physical properties of these systems were investigated and the chain structures 4 and 5 were found to be reminiscent of the parent [Pt2ACHTUNGTRENUNG(EtCS2)4I] species. However, they were more sensitively dependent on the localised nature of the charge on the Ni ion, which caused spont…

Optical Absorption of Zinc Selenide Doped with Cobalt (Zn1-xCoxSe) under Hydrostatic Pressure

2000

Optical absorption of the diluted magnetic semiconductor Zn 1-x Co x Se (x = 0.02) has been measured at room temperature under hydrostatic pressure up to 14 GPa in a membrane diamond-anvil cell. We found two absorption features: (i) an absorption structure in the energy range 1.5 to 1.8 eV, with a negligible pressure shift (i.e. (0.45 ± 0.05) meV/GPa) which we have identified as the Co 2+ (3d 7 ) internal transition 4 A 2 (F) → 4 T 1 (P) and (ii) an onset in the energy range 2 to 2.7 eV which redshifts with pressure (dE/dP = (-8.1 ± 0.6) meV/GPa). We have attributed such absorption edge to charge transfer between the ZnSe valence band and the Co 2+ (3d 7 ) levels. On the assumption that tho…

Polymerisationskinetische und konduktometrische messungen an polystyrylionenpaaren in einem größeren temperaturbereich

1974

Messungen der Bruttogeschwindigkeitskonstante von Polystyryl-Natrium in 3-Methyltetrahydrofuran (3-Me-THF) in Abhangigkeit von der Konzentration der “lebenden” Kettenenden und der Natriumionen ergeben, das die Monomeraddition wie in anderen polaren Losungsmitteln nach einem Mehrwegmechanismus erfolgt. Der Ubergang vom Kontakt- zum solvatgetrennten Ionenpaar wird in einem Temperaturbereich von — 110 bis +85°CC mit Hilfe kinetischer Messungen im Stromungsrohr und durch Leitf ahigkeitsmessungen verfolgt. Analog zu entsprechenden Untersuchungen in Tetrahydrofuran kann dabei die Polymerisation uber jeweils eine Art von Ionenpaaren fast vollstandig isoliert beobachtet werden. Die thermodynamische…